By Howard Deevers
Most of my troubleshooting is done with tools: Voltmeter, Amp Meter, Torque Wrench, or other tools that you would use to check for problems. What does the “nose” have to do with it?
Have you ever gotten into your car and started it, then smelled anti-freeze? I hope not, but anti-freeze has an odor that you will notice immediately. Usually that means that you have a leak in your radiator, in a hose, or a gasket, or somewhere in the cooling system of your car. Service is going to be required soon, or you could be stranded with an overheated engine.
Of course, our air-cooled aircraft engines don't use anti-freeze, so we won't be smelling something like that in our airplanes, but there are plenty of other things that can give off an odor that we don't smell often. Hot oil has an odor. Our brake fluid has an odor. Fuel has an odor. An overheated electrical circuit can give off an odor.
We are all familiar with the odor of fuel during pre-flight, (or at least you should know what it smells like.) But you should not detect the smell of fuel inside the cabin of the airplane. If you do detect the smell of fuel, it might be a good idea to find out where that is coming from. A fuel leak in any fuel line could lead to that moment when the engine gets real quiet while flying. You may think you have plenty of fuel for your flight, but an undetected fuel leak could cause you to make an off-airport landing, after the engine quits due to fuel starvation.
An oil leak, even oil seeping from around the base of a cylinder, can have that distinctive 'hot oil odor.' Adding oil to the engine during pre-flight and again after only an hour of flight might be a tip off that there is an oil leak, or seepage somewhere on the engine. If oil does leak and drips on a hot exhaust pipe or muffler, it will not only give you that 'hot oil' smell but could also contribute to a smoke trail coming from your plane. Unless you are flying in an air show, you really don't want a smoke trail coming from your plane.
Electrical fires are about as bad as an engine fire. An overheating electrical circuit can cause the insulation on the wire to get hot, and in some cases, melt. Electrical overloads give off another distinctive odor. Notice that I said “overloaded.” Many people refer to any electrical problem as a “short.” I have worked with high and low voltage electrical equipment, control systems, and fire alarms most of my working life. I can't tell you how many times people would try to describe an electrical problem by saying “it has a short in it.” I have to explain to them that a 'short' is when the positive and the negative wires come together, or the positive goes to ground. If that happens then the circuit is overloaded, and the fuse in the circuit would open, stopping all electrical current flow. A circuit with an improper fuse could just allow the current to flow and heat the wire and insulation. You would notice an odor.
Electrical problems are not just from wires. There are lots of circuit boards in our navigation and communications radios containing transistors, capacitors, and other circuits that can fail. When they do fail, there is usually a distinct odor. Resetting the circuit breaker or replacing the fuse won't fix it. So, if you do smell that “hot wire” odor, turn of as much of the electrical equipment as you can. If you are flying IFR declare an emergency, and plan for a landing as soon as practical. If you are VFR look for a place to land as soon as practical. Any fire in the cabin of an airplane IS an emergency.
My son lives in Eastern Ohio. He drove his car across town to shop for something. Getting back into his car he notices a “hot” odor. He got out and walked around the car. One of the rear wheels on his car seemed to be hot. Still able to drive the car, he took it to a nearby shop that he knew. They found a stuck caliper on that wheel that was causing the brake to drag; not enough to stop the car, but certainly enough to generate heat. Not a big deal on short trips around town but could have caused him big problems had he been on the Interstate highway and miles away from home and services. His nose tipped him off that something was not right.
Odors aren’t the only indication of a potential problem. Anyone who has done night flight will tell you that the airplane makes different noises at night. That is almost a 'standard' joke in flying. I think that we have an elevated sense of awareness during night flight, and we might hear things that are always there, but just noticed them more at night. In any case, if any really unusual noise does get our attention, start thinking about landing soon.
There are many subtle indications that something might not be normal in our airplanes. These can come from odors, vibrations, noises or just “that doesn't seem right” feelings. Another way to say that is “gut feeling” or intuition. The point here is to pay attention to those indications in aviation. It is better to find them while on the ground, but sometimes they don't let us know until we are in the air. That is why we train for emergencies and attend safety seminars.
Look for your next ARIZONA PILOTS ASSOCIATION safety seminar in person, or online. They are free and help with your WINGS program. And don't forget to 'Bring your wing-man.'